In systems for tapping kegs of fluid and particularly containers of beer there has been used a valve assembly secured to the top of the keg for providing access to the fluid ultimately to be delivered from the keg to a remote position for distribution. Typically, the valve assembly includes a dual valve arrangement with a siphon tube which extends from the valve assembly to the bottom of the keg. The valve assembly is fixed within the keg neck or other valve receiving member to provide a valved access to the fluid once it is pressurized. The valve system, when tapped by a coupler or some other keg tapping means connected to a pressure source, allows pressurized gas to flow into the keg until the desired pressure within the keg is achieved to force the fluid out of the keg through the valve system and ultimately to a distribution device where the fluid can be used to fill glasses and the like. The valve system is one which allows the pressurized gas, usually carbon dioxide, to be forced into the keg but only allows the fluid to be forced out of the keg to distribution device until the keg is entirely emptied of fluid.
The valve assembly includes a body portion which carries an O-ring in sealing engagement with the keg neck to prevent leakage along the interface between the valve body and the neck. To achieve the seal, the O-ring is maintained in a deformed disposition between two metal shoulders of the valve body portion and the keg neck. In units presently available, metal shoulders are moved toward each other to compress the O-ring seal by a threaded fitting threadedly engaged with the keg neck. As the threaded fitting is turned down, the shoulders rotate relative to each other and simultaneously move downward lineally to deform the O-ring between the valve body and the keg neck. The more the fitting is rotated, the more lineal thrust is imparted to the O-ring deforming it even further.
The problem with this approach is that there is no effective way to limit the compression imparted to the sealing ring. Without such a limitation the sealing ring can be over compressed where it will be subjected to "compression set" in which case the seal will not return substantially to its uncompressed state when the lineal thrust is reduced. This detracts from the ability of the O-ring to maintain its sealing characteristics over a long period of time. Also, the sealing ring may be damaged by action of the shoulders rotating against the surface of the seal thereby negating its sealing properties.
Besides the loss in the efficacy of the seal due to overcompression or damage caused by the rotation by two metal parts, the threads can be loosened after continued use allowing the seal to be violated inadvertently. In addition, a rotation movement is usually employed in attaching a tapping member or a coupler to the valving system. Where threaded fittings are used it is quite easy for the turning of the tapping devices to also rotate the threaded fittings thereby unscrewing one fitting relative to the other moving it lineally away from the O-ring allowing the seal to be violated.
Some valve assemblies used with kegs have included a dual valve system having two valve members each biased into engagement with its respective valve seat. To bias at least one of the valve members, a helical spring circumscribing the siphon tube is utilized. A spring retaining cup is used to hold the helical spring in place with sufficient compression to maintain the valve in a normally closed position. The cup extends downwardly from the valve body about the helical spring and has a radially projecting surface extending inwardly toward the siphon tube to support the bottom of the spring. By having the helical spring disposed in this manner, it becomes difficult to clean, allowing residue to build up in the spring coils. Because the cleaning fluids are injected under pressure through the valves, the location of the helical spring adjacent the siphon tube is one which is not readily accessible to the path taken by pressurized cleaning fluid. In addition, by being enclosed by the cup portions, the coils of the spring are not sufficiently exposed to receive the full effect of the cleaning fluid. Where the residue is not completely cleaned away, it can adversely affect the quality of fluid added to the keg for later distribution.
With regard to the coupler or other tapping mechanism, they are inserted by rotation into the valve assembly. Then by separate action, the handle is actuated to open the valves and permit the flow of fluid into and out of the keg in the appropriate channel. After the fluid has been completely dispensed from the keg, the reverse sequence is followed to reseal the valves. If the aforementioned sequence is followed, there will be no loss of fluid or gas in the tapping or untapping procedure.
However, if the handle is inadvertently placed in the tapped or valve open position prior to attaching the coupler to the valve assembly, the valves will be moved to an open position before the coupler is fully in place allowing some leakage to occur until the coupler rotated sufficiently to seal the interface between the coupler and valve assembly. Similarly, if the handle is not relocated to close the valves prior to untapping, leakage will occur until the coupler is rotated out of the valve assembly to a position where the valves reach their naturally closed position. Particularly where the keg contains toxic or otherwise dangerous fluid, the leakage occurring from failure to follow the correct tapping and untapping procedure constitutes a physical danger to the operator. For example, where the keg contains concentrated agricultural chemicals, such as pesticides, insecticides, fertilizer, etc., leakage of these chemicals through an improper coupling technique can be seriously deleterious to the health of the operator.